1. Field of the Invention
The present invention relates to an encoder which detects a position or the like of a detection target.
2. Description of the Related Art
There have been proposed various kinds of encoders which detect, e.g., a movement position of a linearly movable body or a rotational position of a rotationally movable body such as an optical encoder, a magnetic encoder, an electrostatic encoder and others. For example, in an encoder proposed in Jpn. Pat. Appln. KOKAI Publication No. 10-253392, a specification of the encoder can be readily changed by adopting a detachable signal processing circuit which digitizes an analog signal detected by a sensor. FIGS. 20A and 20B show block diagrams of such an encoder.
FIG. 20A shows an example of an encoder having a signal processing circuit 103 attached in a sensor head 101. In this example, two-phase analog signals (FIG. 20A shows one signal alone) according to movement of a detection target are output to the signal processing circuit 103 from a sensor signal detection amplification circuit 102. Here, the two-phase analog signals are generally periodic signals whose phases are shifted by 90 degrees with respect to each other.
The signal processing circuit 103 is a circuit which digitizes the two-phase analog signals which are input thereto. Here, the signal processing circuit 103 has an interpolation division circuit which subjects to interpolation division processing the analog signals which are input thereto. An interpolation position in one cycle of the analog signal can be obtained by the interpolation division circuit. For example, assuming that the two-phase analog signals are an A phase analog signal (Vsinθ) and a B phase analog signal (Vcosθ) which are generally used as encoder signals and Va and Vb are values obtained by converting these analog signals into digital signals, the interpolation position in one cycle can be obtained based on the following expressions:Va/Vb=V sin θ/V cos θ=tan θθ=tan−1(Va/Vb)
After the analog signals are digitized in this manner, the digital signals are output to a control device 104 from the sensor head 101.
On the other hand, FIG. 20B shows an example of an encoder in which a signal processing circuit 103 is provided in a control device 104. In this example, the signal processing circuit 103 is not attached in the sensor head 101. That is, in the example of FIG. 20B, after the analog signals are output to the control device 104 from the sensor head 101, they are digitized by the signal processing circuit 103 in the control device 104.
Here, in the encoder proposed in Jpn. Pat. Appln. KOKAI Publication No. 10-253392, a plurality of signal processing circuits must be prepared in advance in accordance with a signal input specification of the control device 104. That is, in order to cope with a specification which is not previously prepared, a signal processing circuit which can support this specification must be additionally manufactured.
Further, when a cyclic pattern of a scale is, e.g., 20 μm, signals in various output modes, e.g., a low-resolution digital signal output mode with a resolution of approximately 5 μm, a high-resolution digital signal output mode with a resolution of approximately 1 μm and an AB phase analog signal mode which does not perform digital conversion are required based on the use application of an encoder, the specification of a control circuit 105 or the like at that time in accordance with the intended use. It is preferable that such signals in various output modes can be generated and output by one type of sensor head.